1.Throw an error whenever the user try to delete the contact which is not associated to any account (when AccountId is null) how to write apex class and test class foe above requirement

Here it is

@isTest
public class ContactTrigger_Test {
    static testMethod void test_contact_cannot_detele_without_account(){
        Contact contact = new Contact(LastName = 'Test');
        insert contact;
        try {
        	delete contact;
        } catch (Exception ex){
            system.assert(ex.getMessage().contains('Cannot delete without AccountId.'));
        }
    }  
}